Instantaneous circuit interrupters (also called instantaneous circuit breakers) and overload circuit interrupters (also called overload circuit breakers) are important components used to protect electrical circuits. Often, an instantaneous circuit interrupter and an overload circuit interrupter are packaged in a single device simply called a circuit breaker. Typically, a plurality of such combination-circuit-breaker devices are installed in a “breaker box” or “panel” used to protect a corresponding number of electrical circuits in a house or building.
Instantaneous circuit interrupters supply a means of interrupting current that might be dangerous to people or the wiring circuit, as in the case of a short-circuit overcurrent that could result in a fire or electrocution. An instantaneous circuit interrupter typically employs an electromagnet switch to open immediately (with no intentional time delay) when a high multiple of the rated current is sensed. On the other hand, an overload circuit interrupter typically employs a bimetal strip switch to open after a slight delay (with an intentional time delay that is inversely proportional to the amount of overcurrent) when a low multiple of the rated current is sensed. A third type of circuit protection interrupter, called a GFCI (Ground Fault Current Interrupter, also known as GFI) interrupt current being drained off a circuit to ground that could present a shock hazard to people. Often a combination of an instantaneous circuit interrupter, an overload circuit interrupter device and a GFCI device are incorporated serially in the same circuit or combined into a single unit.
There are three basic situations where circuit interrupters come into play and open the circuit. First when there is a short circuit causing a sudden very high surge of current. This should trip the instantaneous circuit interrupter. Second when there is an ongoing load that draws more current than the interrupter is rated for. This should trip the overload circuit interrupter. Third, when there is some current being drawn off to ground. This should trip the GFCI.
In each of these situations there are very definite specifications as to how long the interrupter has to respond. It is essential that these devices operate within these parameters, either to open quickly as in a short circuit or an improper ground, or relatively slowly as in the case of a smaller overload. For instance in the latter situation where, when a motor is starting up, the motor may draw a much higher current for a short period of time. It would be inconvenient to have the breaker tripping at these times. Thus, circuit breakers have an overload circuit interrupter employing a thermal element that allows small overcurrents for limited time periods. But in the case of a short circuit or a ground fault it is essential that the breaker interrupt the current flow as quickly as possible, generally within a few cycles of AC power.
Each of these sensing capabilities can function independently of each other. For instance, a short circuit can trip a circuit breaker (i.e., the instantaneous circuit interrupter) in a panel while the GFCI upstream of it is unaffected. Similarly, an extended overcurrent can cause the thermal portion of a circuit breaker to unlatch while the GFCI remains unaffected. Finally, a GFCI can trip while the circuit breaker downstream remains in the closed position. The capability of tripping as quickly as possible is called the instantaneous tripping response.
Conventional circuit breaker testing devices suffer by only testing either circuit breakers or GFIs. Ideally one device should be able to test either selectively and separately.
Devices heretofore known suffer from one or more of the following disadvantages:
(a) the circuit breaker is not predictably tripped;
(b) a part of the device is consumed in use, as with an internal fuse blowing;
(c) requiring the user to travel back and forth between the circuit breaker panel and the point in the circuit where one wishes to work;
(d) switching off and on of multiple circuit breakers, which will affect appliances on those circuits;
(e) requiring two devices, a transmitter and a receiver;
(f) removal of the breaker from the panel;
(g) does not switch off the breaker from the location where one wishes to work;
(h) tests and trips a GFI device but not the circuit breaker protecting that GFI device;
(i) tests the thermal sensor of the circuit interrupter as opposed to the instantaneous magnetic tripping capability of the interrupter;
(j) overstresses the circuit by drawing more wattage (volts times amps) or power (volts times amps times time) than actually required for such a test;
(k) cannot be used at any point in the circuit of the circuit breaker;
(l) potential damage to wiring and the device in the event of the circuit breaker not tripping off;
(m) excessive heat being dissipated during the time it normally takes the breaker to trip;
(n) damage to switch contacts due to arcing;
(o) tests either only a circuit breaker or a GFCI, but not either selectively (this means two separate devices are required instead of one);
(p) does not test if the circuit interrupter is operating within prescribed specifications, but only if it functions at all;
(q) does not incorporate an interrupter within the device that will respond to various dangerous situations such as the device's switch fusing closed while there is a load of sufficient magnitude to present an overheating condition in the wiring of the circuit or in the device itself;
(r) incorporates an interrupter within the device that may blow during normal operation of the device's testing procedure;
(s) incorporates an interrupter within the device that will not respond to a load of sufficient magnitude to prevent an overheating condition in the wiring of the circuit or in the device itself; and/or
(t) contains a fuse that may blow during testing that is within the interrupter's specified operating range (for instance, an 800-amp current for ½ cycle of AC power) or would not respond in a potentially dangerous situation (for instance, a 40-amp overload of extended duration on a 20-amp circuit).